AU2017204580B2

AU2017204580B2 - A method of recovering a substance

Info

Publication number: AU2017204580B2
Application number: AU2017204580A
Authority: AU
Inventors: Mark Fritz; Ben Ziegelaar
Original assignee: Australian Minerals Res Pty Ltd
Current assignee: Australian Minerals Research Pty Ltd
Priority date: 2016-07-04
Filing date: 2017-07-04
Publication date: 2021-11-04
Anticipated expiration: 2037-07-04
Also published as: AU2017204580A1

Abstract

The present disclosure relates to the recovery of substances from what might be considered a waste product, 5 such as fused samples that would typically be discarded from analytical laboratories. The recovered substances can then be reused. To that end, disclosed is a method of recovering a substance from a sample comprising a flux material, the method comprising: obtaining a sample that 10 has been prepared for compositional assay, the sample comprising a mineral and a flux material; adding the sample to a solvent so that the substance dissolves at least partially in the solvent, resulting in (a) a solution comprising the dissolved substance, and (b) a 15 solid precipitate; and separating the solution from the precipitate.

Description

A METHOD OF RECOVERING A SUBSTANCE

Field of Technology

The present disclosure relates to a method of recovering a substance from a sample comprising a flux material, for example a mineral sample prepared for compositional assay.

Background

Analytical laboratories typically use a flux to prepare a fused glass sample, hereafter referred to as a "bead", containing a mineral sample for composition analysis, for example x-ray fluorescence (XRF) spectroscopy. Alternatively, the use of flux can produce a solution, which can then be analysed with other techniques such as plasma spectrometry.

Summary of Disclosure

After completion of the analysis the fused glass beads or waste solutions are typically discarded either immediately or after a limited storage time to landfill or liquid waste disposal. The beads or solutions usually contain around 7 grams of flux. It is estimated that Australia alone produces some 30 tonnes of waste fused beads per annum.

In broad terms, the present disclosure relates to the recovery of substances from what is considered a waste product, for example, fused samples that would typically be discarded from analytical laboratories. The recovered substances can then be reused.

According to a first aspect, the present invention provides a method of recovering a substance from a sample comprising a flux material, the method comprising: obtaining a sample that has been prepared for compositional assay, the sample comprising a mineral and a flux material; adding the sample to a solvent so that the substance dissolves at least partially in the solvent, resulting in (a) a solution comprising the dissolved substance, and (b) a solid precipitate; and separating the solution from the precipitate.

According to a second aspect, the present invention provides a method of recovering a substance from a sample comprising a flux material and a material for compositional analysis, the method comprising: adding the sample to a solvent so that the substance dissolves at least partially in the solvent, resulting in (a) a solution comprising the dissolved substance, and (b) a solid precipitate; and separating the solution from the precipitate.

According to either the first or the second aspect, the precipitate may contain the substance sought to be recovered.

The flux material may be a borate-based flux material, such as a lithium tetra-borate, lithium meta-borate, or a mixture thereof. For example, the flux material may comprise approximately 35.3% lithium tetra-borate and approximately 64.7% lithium meta-borate.

The solvent may comprise water or other polar solvents. The substance may be dissolved in the solvent at a temperature of between 600C and 105°C.

The step of separating the solution from the precipitate may comprise passing at least a portion of the solution through a filter. Alternatively or additionally, the step of separating the solution from the precipitate may comprise allowing the precipitate to settle in the solution and then decanting at least a portion of the solution. The settling may occur below a boiling point, e.g. less than 1000C. A flocculating agent may be used to enhance the settling of the precipitation.

After decanting at least a portion of the solution above the precipitate, the method may comprise passing a remaining portion of the solution through a filter to separate from the precipitate. The filtrate may then be combined with the decanted solution.

However the solution (comprising the dissolved substance) is separated from the precipitate, the method may then comprise allowing crystals of the dissolved substance to form in the solution. This can be done by allowing the solution to cool. The salt crystals can then be separated from the remaining solutions, and processed further to ensure that its composition meets desired specifications.

The substance sought to be recovered from the sample may comprise lithium and/or boron compounds. For example, the recovered substance may be lithium meta-borate, lithium tetra-borate or lithium carbonates, depending on the flux that was used and the dissolution processes invoked. Alternatively, sodium meta-borates and tetra-borates may be recovered from fused samples containing sodium borate flux.

Embodiments of the disclosed method may provide the advantage of recycling potentially tonnes of fused samples per annum that would otherwise be discarded after analysis. Useful substances found in the sample can therefore be recovered and repurposed. For example, if the sample was fused with lithium borate flux, lithium and boron can be recovered and reused again as a flux or in other applications. Lithium can for example also be used in batteries. Also disclosed is a method of recovering a desired substance from a sample comprising a flux material, the method comprising: obtaining a sample that has been prepared for compositional assay, the sample comprising a mineral and a flux material, such as a borate-based flux material; adding the sample to a solvent so that the sample dissolves at least partially in the solvent, resulting in (a) a solution, and (b) a solid precipitate, wherein either the solution or the solid precipitate comprises a majority of the desired substance; and separating the solution from the precipitate.

The mineral may for example be a valuable metal, such as gold, silver or platinoid, or rare earths.

Brief Description of Drawings

Figure 1 is a flow chart of a method according to an embodiment of the present disclosure.

Figure 2 is a flow chart of a method according to an embodiment.

Figure 3 is a flow chart of a method according to another embodiment.

Figure 4 is a flow chart of a method according to further embodiments.

Figure 5 is a flow chart of a method according to another embodiment.

Figure 6 is a flow chart of a method according to a further embodiment.

Detailed Description

Throughout the specification, unless the context otherwise requires, the terms "flux", "flux material", or variants thereof, refers to a chemical agent used to facilitate melting, solubility or fusion, particularly in the context of preparing fused samples or solutions for compositional analysis. In the context of preparing solutions for compositional assay, the flux may allow normally insoluble substances to become soluble. Examples of flux include but are not limited to lithium borates and sodium borates.

Also throughout the specification, unless the context otherwise requires, the term "fused sample" refers to a sample, such as a mineral sample, that has been prepared for compositional assay by melting the sample typically with the aid of a flux material to form a homogenous mixture.

Figure 1 shows a method 100 of recovering a desired substance from a sample comprising a flux material. The method comprises obtaining a sample that has been prepared for compositional assay, the sample comprising a mineral and a borate-based flux material (step 110). In this example, the sample is a fused sample. The method then comprises adding the fused sample to a solvent so that the substance dissolves at least partially in the solvent (step 120), which results in (a) a solution comprising the dissolved substance, and (b) a solid precipitate. Then, the method comprises separating the solution from the precipitate (step 130).

The recovered substances can be in the form of sodium borates, lithium borates and/or lithium carbonate. In Australia, the most common flux used is 12:22 which contains 35.3% lithium tetra-borate and 64.7% lithium meta-borate. This flux is extensively used in the analysis of iron ore, bauxite, cement, noble metals, mineral sand and nickel ores.

In step 110, according to this specific embodiment, the fused sample is in the form of a glass bead. However, it will be understood that in other embodiments the sample may be a solution. The glass beads are typically obtained from analytical laboratories.

In step 120, the glass bead is digested in a solvent to produce a solution and a solid precipitate. The solvent may be a polar solvent, such as hot water. As a result of the digestion, most of the flux is dissolved while the minerals that were assayed form a precipitate.

In step 130, separating the resulting solution (containing at least some of the flux material) from the precipitate (containing the mineral) allows the flux material and/or mineral to be reused.

With reference to Figure 2, a method 200 is shown according to a further embodiment. In step 108, different types of fused samples are first sorted according to classes of minerals or fluxes in order to simplify the recovery process and/or improve the purity of the ultimately recovered substance. A certain group of fused samples is then selected in step 110a for further processing. In this embodiment, the fused samples selected are glass beads comprising lithium borate flux.

In step 120a, similar to step 120, the glass bead is digested at atmospheric pressure or increased pressure in the solvent (in this example, water) heated to a temperature between 800C and 1050C. Preferably, the solvent is heated to 1000C or thereabouts. This causes the majority of the lithium borates to dissolve, resulting in an alkaline solution due to the presence of lithium oxide, which causes transition metals (e.g. iron, nickel) to precipitate as hydroxide flocs, thus forming a solid precipitate in step 120a.

In step 130a, separating the solution from the precipitate comprises the step 132 of allowing the precipitate to settle. Additionally, a flocculating agent may be added (step 133) to assist in settling the precipitate. Once settled, the supernatant liquid (i.e. the liquid lying above the settled precipitate) can be decanted. Alternatively, the supernatant liquid may be removed by siphoning or other suitable means. The supernatant liquid is typically clear.

Then, in step 136, the remaining portion of the solution (after decanting, siphoning etc.) can be passed through a filter to separate from the precipitate. Preferably, the solution is hot filtered. The precipitate or residue may be set aside for further processing (which will be described below with reference to Figure 4). The filtrate can then be combined with the supernatant liquid that was decanted. The combined solution can proceed to the crystallisation process (see Figure 3) to recover lithium borate salts. Alternatively, the supernatant liquid may proceed straight to the crystallisation process. As another alternative, instead of the steps 132 and 134, the solution from step 120a can be passed directly through a filter to separate from the precipitate. However, performing the step of decanting or otherwise removing the supernatant liquid will reduce the amount of filtration time.

Figure 3 shows a crystal harvesting and processing method 300 to obtain lithium borate salts or crystals from the solution resulting from step 130a. Step 302 of filtering the solution may be the same as step 136 (from Figure 2), or may occur directly after the step 120a of digesting the glass bead. Either way, the filtrate obtained in step 304 is a solution separated from any residue as a result of digestion of the bead in the solvent. The solution is then cooled in step 306 so that the lithium borate in the solution precipitates or crystallises in step 308.

In step 310, the remaining filtrate, i.e. the supernatant liquid lying above the crystals, is decanted or otherwise separated from the crystals, and may be set aside for further processing. In one example the further processing includes analysing the filtrate for residual lithium borate salts and impurities (see steps 410, 412a/b, 406 and 414 of Figure 4, which will be described in more detail below).

On the other hand, the crystals produced from step 308 may undergo a crystal purification process in step 312. This may be done to ensure that the crystals meet specification suitable for the end product the crystals. The purification process may involve re-crystallisation by redissolving the crystals in the solvent at high temperatures, and then cooling the solution to allow the crystallisation. The crystals may then be washed with an alkaline solution, preferably a mildly alkaline solution.

In step 314, the crystals are then dried, which is preferably done at or above 2000C, to produce a white powder. In step 316, the dried powder is then tested for quality control purposes. Such testing may involve analysis by XRF, inductively coupled plasma mass spectrometry (ICP-MS) and/or x-ray powder diffraction (XRD). Lithium and/or boron concentrations, or the lithium to boron ratio, can then be adjusted in step 318 to achieve the desired end product specification.

In step 320, the crystals are then subjected to calcination (i.e. heated to high temperatures, such as 800°C-1050°C, in oxygen or air). During this process the crystals may be placed in in suitable containers made of inert material such as graphite, platinum or alloys thereof. At this phase adjustments may be made to lithium and or boron oxide concentrations to achieve the desired end product. The resulting substance can then be crushed and/or sieved (step 322) and packaged (step 324) as a product.

Turning back to step 130a, while the resulting solution from step 130a progressed to the crystal harvesting and processing method 300, the precipitate may also be processed further to extract any residual lithium or other desired substance if a significant amount of lithium or boron remains. With reference to Figure 4, in one embodiment the precipitate is collected (step 402), treated (step 404), and re-digested (step 406). In step 404, the treatment may comprise calcination and further extraction after pH adjustment. The precipitate can then undergo another digestion phase (step 406) in the solvent at a supercritical temperature, for example 1500C. After digestion, a residue is formed (step 408).

Additionally, as previously mentioned the supernatant liquid separated from the crystals in step 310 can also be analysed for residual lithium borate or impurities. Thus, with reference to Figure 4, this may comprise collecting the supernatant liquid (step 410), modifying the pH of the liquid (since the liquid may be highly alkaline) and testing the liquid to determine whether it requires lowering of impurities (step 412a). If so, the impurities are bled (step 412b). It is believed that if the flux material used comprises approximately 35.3% lithium tetra borate and 64.7% lithium meta-borate, it is possible to recover an amount of lithium tetra-borate and lithium meta-borate within approximately 10% of the original amounts.

The lithium and boron recovery process described above can treat all lithium or other borate based fluxes. Laboratories may also use sodium-borate salts for the above applications. When this is used only purified sodium borate salts will be recovered.

With reference to Figure 5, a method 500 for recovering lithium carbonate is shown according to another embodiment of the present disclosure. Like the method 200, in this embodiment, the method 500 involves sorting glass beads (step 108) to obtain beads comprising lithium borate flux (step 110a). However, in step 120b, digestion of the glass beads in the solvent is done at moderate pressure up to 1500C under carbon dioxide atmosphere. This results in the conversion of lithium salts to lithium bicarbonates. Then, as in the method 200, step 130b involves separating the solution from the precipitate by allowing the precipitate to settle (step 132), which may involve the use of a flocculating agent (step 133), and decanting at least some of the supernatant liquid (step 134).

This produces a solution containing lithium carbonate and a residue or precipitate. The residue is then processed further in steps 504 to 508. The solution is also processed further (see step 502, and steps 602 to 612 in Figure 6).

In step 502, the solution is allowed to cool, for example to near or below 00C, so that the lithium carbonate crystallises. Continuing onto Figure 6, in step 602, the liquid and crystals from step 502 are then separated, for example by filtration. The crystals undergo further processing in steps 604 to 608, while the liquid is processed according to steps 610 and 612.

The crystals are subjected to quality control (step 604). If the quality of the crystals are within the desired specification, the crystals are dried (step 606), but if not the crystals undergo further purification (step 608). On the other hand, in step 610 the liquid or filtrate is cooled and its pH may also be adjusted, which results in the crystallisation of boric acid in step 612.

Turning back to the precipitate or residue from step 130b, in step 504 the residue is analysed to determine whether there is any significant residual lithium. If not, the residue is disposed in step 508. If so, the residue undergoes a calcination procedure in step 506 to optimise lithium borate recovery.

It will be understood to persons skilled in the art of the invention that many modifications may be made without departing from the spirit and scope of the invention. For example, according to yet another embodiment the method may be used to recover sodium meta-borates and tetra borates from samples fused with sodium borate flux.

In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

Claims

Claims 1. A method of recovering a substance selected from lithium borate, sodium borate or lithium carbonate from a sample comprising a flux material, the method comprising: obtaining a fused sample that has been used for compositional assay and is now considered a waste product, the sample comprising a mineral fused with a flux material;

adding the fused sample to water so that the substance dissolves at least partially in the water, resulting in (a) a solution comprising the dissolved substance, and (b) a solid precipitate; and

separating the solution from the precipitate and collecting the solution for further processing.
2. The method of claim 1 wherein the flux material is a borate-based flux material.

3. The method of claim 1 or 2, wherein the substance is dissolved in water at a temperature of between 80C and 105C.

4. The method of any one of the preceding claims, wherein the solution that has been separated from the precipitate is allowed to cool, thus causing substance to precipitate.

5. The method of claim 4, comprising recovering the substance for reuse.

6. The method of any one of the preceding claims, wherein the step of separating the solution from the precipitate comprises passing at least a portion of the solution through a filter.

7. The method of any one of claims 1 to 5, wherein the step of separating the solution from the precipitate comprises allowing the precipitate to settle in the solution and decanting at least a portion of the solution.

8. The method of anyone of the preceding claims, comprising using a flocculating agent to enhance the settling of the precipitate.

9. The method of claim 7 or 8, wherein after decanting at least a supernatant portion of the solution, the method comprises passing a remaining portion of the solution through a filter to filter out the precipitate, and subsequently combining the filtrate with the decanted solution.

10. The method of any one of the preceding claims, wherein the substance that is dissolved comprises lithium tetra-borate and or lithium meta-borate.

11. The method of any one of the preceding claims, wherein the substance that is dissolved comprises sodium tetra-borate and or sodium meta-borate.

12. The method of any one of the preceding claims, wherein the method further includes recovering the (b) solid precipitate and analysing it to determine whether there is significant trace amounts of the substance being recovered.

13. The method of claim 12, wherein if the analysing step identifies significant trace amounts of the substance being recovered, subjecting the solid precipitate to one or more further processing steps to recover the substance.

14. The method of claim 13, wherein the one or more further processing steps include calcination.

15. The method of any one of the preceding claims, wherein the mineral comprises one of: gold, silver or platinoid, and rare earths.

110 2017204580

Obtain fused sample containing flux

Results in: 120 Add fused sample to solvent 1. Solution comprising to dissolve substance dissolved substance.

2. Solid precipitate. 130 Separate solution from precipitate

FIGURE 1

9220928_1 (GHMatters) P102791.AU.1

200 Sort fused samples

110a 2017204580

Obtain fused sample(s) 122a comprising lithium borate flux Heat water to between 80°C 120a and 105°C

Digest fused sample in water to dissolve lithium borate Results in: 130a 1. Solution comprising dissolved lithium borate. Separate solution from precipitate 2. Solid precipitate. 132

Allow precipitate to settle Add flocculating agent to enhance settling 134 133 Decant at least some of solution

136

Pass remaining portion of solution through filter

FIGURE 2

9220928_1 (GHMatters) P102791.AU.1

304 302 2017204580

312 306 308 310

314 318 316

320 322

300 324

FIGURE 3

9220928_1 (GHMatters) P102791.AU.1

402 410

Collect Supernatant precipitate from liquid from step step 130a 310 412b 2017204580

Bleed 404 412a impurities

Treat Requires precipitate lowering of Yes impurities?

No 406

Digestion

408 414

Residue Residue

FIGURE 4

9220928_1 (GHMatters) P102791.AU.1

Sort fused samples 500 110a

Obtain fused sample(s) comprising lithium borate flux 122b

120b At moderate pressure up to 2017204580

150° under CO2 atmosphere Digest fused sample in water to dissolve lithium borate 130b Results in lithium bicarbonates Separate solution from precipitate 132 133

Allow precipitate to settle Add flocculating agent to enhance settling 134 504 Decant at least some of 508 Residue analysis solution

Dispose 502 Significant residual No Allow lithium carbonate to lithium? crystallise in solution 506 Yes Calcination of residue

FIGURE 5

9220928_1 (GHMatters) P102791.AU.1

608 604 602 2017204580

606 610

612

600

FIGURE 6

9220928_1 (GHMatters) P102791.AU.1